In situ combustion of stratum having an exposed face



- Aug. 11, 1959 F. w. CRAWFORD 2,899,186

IN SITU COMBUSTION 0F STRATUM HAVING AN EXPOSED FACE Filed May 19, 1958 INVEN R.

F. W CR FORD A T TORNEVS nite 2,899,186 Patented Aug. 11, 1959 IN SITU COMBUSTION OF STRATUM HAVIN AN EXPOSED FACE Francis W. Crawford, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application May 19, 1958, Serial No. 736,281

Claims. (Cl. Z623) States Patent Qfiice drive process, upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein, followed by injection of air thru the ignition borehole in the stratum, constitutes a direct air drive process for cifecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum frequently plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and to permit the continued progress of the combustion zone thru the stratum, inverse air injec tion has been resorted to. By this technique, a com bustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes. In situ combustion techniques are also being applied in the gasification of coal.

When conducting field operations in hydrocarbon production by in situ combustion, it is occasionally desirable to produce the hydrocarbons from a location near an outcropping, an open mine, or other structure where compressed gases could escape thru an exposed face. In such instances it is necessary to selectively plug the formation near the exposed face to prevent loss of air and produced hydrocarbons thru the face. This invention is concerned with a method for so do ing and for producing hydrocarbons from such a stratum.

Accordingly, it is an object of the invention to provide a process for recovering hydrocarbons by in situ combustion from a carbonaceous stratum having an exposed face or outcropping. Another object is to plug such a stratum in an area extending generally parallel with the exposed face and relatively close thereto. A further object is to provide an in situ combustion process for producing hydrocarbons in a carbonaceous stratum having an exposed face or outcropping without loss of gas pressure and hydrocarbons thru the exposed face and which permits recovery of hydrocarbons within close proximity to the exposed face. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises establishing in situ combustion in a carbonaceous stratum around a line of boreholes generally parallel with anexposed face of said stratum; driving hot liquid hydrocarbons into the stratum intermediate said boreholes and the exposed face, whereby said hydrocarbons are cooled and congeal therein so as to plug the stratum; driving the combustion zone from the line of boreholes to a second line of boreholes more-remote from the face by injecting air or other oxygen-containing, combustion-supporting gas thru the second line of boreholes; and recovering produced hydrocarbons from the first line of boreholes. One method of plugging the stratum comprises initiating combustion in the carbonaceous stratum around each of the boreholes in the first line and thereafter injecting air thru the second line of boreholes whereby produced vaporous hydrocarbons are recovered from the boreholes in the first line and hot liquid hydrocarbons are driven into the stratum intermediate the first line of boreholesfand the exposed face so as to cool therein and plug the stratum, thereby shutting oif flow of gases thru the exposed face. This method of plugging the stratum may be effected by injecting air admixed with a low concentration of fuel gas thru the second line of boreholes until air and fuel gas are being produced thru the first line of boreholes, igniting the gaseous mixf ture while same is slowly flowing into the boreholes in the first line, and heating the wall of each of these boreholes to ignition temperature so that in situ combustion is established around each of the boreholes in the first line. Burning a charcoal bed in the borehole is an excellent method of heating same to ignition tem perature. It is also feasible to establish combustion around each of the boreholes in the first line by any suitable means and drive the resulting combustion zone toward the exposed face of the stratum by direct drive of air injected thru these boreholes while maintaining the boreholes in the second line shut-in or closed, whereby hot tar or other heavy liquid hydrocarbons is driven into the stratum intermediate the first line of boreholes and the exposed face where congealing takes place when these hydrocarbons are cooled in the cool stratum and plug the same.

In accordance with another embodiment of the invention, combustion is initiated around alternate boreholes in the first line and air is injected thru the other boreholes in the line so as to move the combustion front from each ignition borehole outwardly to the adjacent'injection boreholes. When this has been accomplished, air injection thru the second line of boreholes moves the combustion front by inverse drive toward the second line and also drives hot heavy liquid hydro carbons into the cool stratum intermediate the first line of boreholes and the exposed face of the stratum whereby plugging is eifected. Here, again, it is feasible to utilize direct air injection thru all of the boreholes in the first line after the combustion front has been completely established between the boreholes while maintaining the second line of boreholes shut-in as a means of driving liquid hydrocarbons toward the face of the stratum, and, after plugging is effected, injecting air thru the boreholes in the second line so as to move the combustion front from the first line of boreholes to the second line and produce hydrocarbons thru the boreholes in the first line without losing hydrocarbons and gas pressure thru the exposed face of the stratum.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing which is an isometric view of a section of stratum showing an arrangement of boreholes therein in accordance with the invention.

Referring to the drawing, a carbonaceous stratum 10 having an exposed face 12 is penetrated by a first line of boreholes or wells 14, generally parallel with face 12, and a second line of boreholes 16, substantially parallel to the first line. Boreholes 14 are provided with casing 18 and tubing 20, while boreholeslfi are provided with casing 22 and tubing 24. Numeral '26 designates a fire or combustion front around boreholes 14. The line of boreholes 14 are positioned a substantial but short distance from face 12 so that hot liquid hydrocarbons, such as hot tar, driven into the stratum between the line of boreholes and face 12 congeal before passing thru the face thereby plugging the stratum so as to prevent flow of gas thru the face. However, it is desirable to produce as close to face 12 as possible and still provide sufficient stratum between boreholes 14 and the face to provide adequate cooling of the hot liquid hydrocarbons to effect congealing. The spacing between face 12 and boreholes 14 will depend upon the temperature of the stratum and the character of the carbonaceous material in the stratum. This space will generally be somewhere in the range of or 15 feet to 40 or 50 feet. It is generally desirable to utilize a spacing between the individual wells in the line of wells 14 which is at least as short as the distance from these wells to the face of the outcropping so as to facilitate preferential flow of injected air from borehole to borehole in the line. A similar or different spacing of boreholes 22 may be utilized, although the spacing will generally be the same as between boreholes 14. Line of boreholes 16 is substantially parallel to the line of boreholes 14 although some variation in this arrangement is possible without unduly detracting from the recovery process.

The drawing illustrates that embodiment of the invention where combustion is initiated around alternate wells in the line of wells 14, with injection of air thru the remaining wells, whereby the ignition wells become production wells in the initial phase of the process. When the combustion front is moved across from well to well in the stratum, injection of air thru alternate wells 14 is terminated and the combustion front is fed by injecting air thru wells 16 whereby the combustion front moves thru the stratum to the injection wells 16. The gas pressure within the stratum effected by the air injection drives hot liquid hydrocarbons into the stratum intermediate the line of wells 14 and face 12 so as to cool the same therein and cause congealing and plugging. This prevents escape of produced hydrocarbons and/or air thru face 12 and permits recovery of produced hydrocarbons from boreholes 14 thru tubing 20.

As heretofore stated, another technique for producing the stratum shown comprises initiating combustion around each of the boreholes in line 14, as by burning charcoal or other fuel therein, so as to raise the temperature of the stratum around these boreholes to ignition temperature, then contacting the hot stratum with O and then injecting air thru the line of wells 16 so as to move the combustion front thru the stratum between the lines of wells and also to drive hot liquid hydrocarbons into the stratum intermediate line of wells 14 in face 12 so as to plug the same.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing by in situ combustion a carbonaceous stratum having an exposed face which comprises establishing combustion of carbonaceous material in said stratum around a series of boreholes in a line substantially parallel with said face and spaced therefrom a short but substantial distance; driving hot, heavy liquid hydrocarbons from the combustion area toward said face whereby said hydrocarbons cool and become more viscous so as to plug said stratum intermediate said series of boreholes and said face; and moving a combustion front from said line of boreholes to a second line of boreholes more remote from said face and substantially parallel thereto by injecting 0 containing, combustion-supporting gas thru said stratum from said second line of boreholes; and recovering produced hydrocarbons from said series of boreholes.

2. The process of claim 1 wherein combustion is initiated in each borehole of said series and the resulting combustion zones are expanded and driven toward said second line of boreholes by injecting air thru said stratum from said second line of boreholes.

3. The process of claim 1 wherein in situ combustion is initiated around alternate boreholes in said series and air is injected thru the remaining boreholes in said series so as to move the combustion front radially outwardly from each ignition borehole to the adjacent injection borehole; and thereafter injecting air thru said second line of boreholes.

4. The process of claim 3 wherein air is injected thru each of the boreholes in said series after the combustion front has reached the injection boreholes and maintaining said second line of boreholes closed so that the combustion front moves toward said face whereby said stratum becomes plugged before injection of air thru said second line of boreholes is commenced.

5. The process of claim 1 wherein combustion is initiated around each borehole of said series and the resulting combustion zones are driven toward said face by direct drive by injecting said gas thru each said borehole whereby hot liquid tar is driven into cool stratum intermediate said boreholes and said face to cool and plug said stratum.

References Cited in the file of this patent UNITED STATES PATENTS 2,793,696 Morse May 28, 1957 

1. A PROCESS FOR PRODUCING BY IN SITU COMBUSTION A CARBONACEOUS STRATUM HAVING AN EXPOSED FACE WHICH COMPRISES ESTABLISHING COMBUSTION OF CARBONACEOUS MATERIAL IN SAID STREAM AROUND A SERIES OF BOREHOLES IN A LINE SUBSTANTIALLY PARALLEL WITH SAID FACE AND SPACED THEREFROM A SHORT BUT SUBSTANTIAL DISTANCE; DRIVING HOT, HEAVY LIQUID HYDOCARBONS FROM THE COMBUSTION AREA TOWARD SAID FACE WHEREBY SAID HYDROCARBONS COOL AND BECOME MORE VISCOUS SO AS TO PLUG SAID STREAM INTERMEDIATE SAID SERIES OF BOREHOLES AND SAID FACE; AND MOV- 